1. Field of the Invention
The present invention relates to a design support technique for an image forming apparatus.
2. Description of the Related Art
Software controls the operations of various kinds of devices. For example, in an image forming apparatus, in order to convey a recording member (to be referred to as a “sheet” hereinafter) to a predetermined position in a predetermined time using a conveyance mechanism including rollers, guides, and the like, control software controls the conveyance mechanism to convey the sheet. In many sheet conveyance control operations, it rarely suffices to simply convey a sheet at a constant velocity in one direction. For example, software implements the control operation of, for example, detecting the position of a sheet using a sensor, stopping the sheet at a predetermined position, and reversing the conveyance direction of the sheet by reversing conveyance rollers.
FIGS. 15A and 15B are graphs showing an example of conveyance control for a plurality of target conveyance members (sheets 1501 and 1502). FIG. 15A is a graph showing the positions of the leading edges (to be referred to as “leading edges” hereinafter) and the positions of the trailing edges (to be referred to as “trailing edges” hereinafter) of the sheets 1501 and 1502 in a conveyance mechanism in terms of the relationship between conveyance rollers R1 to R4 and the time. Referring to FIG. 15A, “R11” indicates that the leading edge of the sheet 1501 has reached the roller R1 at time t11. The trailing edge of the sheet 1501 reaches the roller R1 at time t12. In this case, the time required for the sheet 1501 to pass through the roller R1 is t12−t11. FIG. 15B is a graph showing the relationship between the driving velocity of the roller R1 and the time. The roller R1 starts rotating at time t0 and reaches a conveyance velocity (target velocity) V1 for conveying the sheet 1501 at time t01. The roller R1 starts decelerating after time t12 when the trailing edge of the sheet 1501 passes through the roller R1.
Referring to FIG. 15A, the leading edge of the sheet 1501 is conveyed to the roller R3 at time t31 (R31). The roller R3 is at rest until time t32 (R32). For example, in conveyance control on the sheets 1501 and 1502 shown in FIG. 15A, for skew correction of each sheet, conveyance is in some cases temporarily stopped to form a loop on the leading edge of each sheet at the roller R3. This temporary stopping state is indicated as a flat state (between the rollers R31 and R32) wherein the conveyance distance does not change between times t31 and t32.
In this case, the conveyance of the sheet 1501 is temporarily stopped at timing R31, and is started at timing R32. After the trailing edge of the sheet 1501 leaves the roller R3 at timing R33 (time t33), it is necessary to stop the roller R3 for skew correction of the sheet 1502 (time t34). The time difference is very small between timing R33 (time t33) when the trailing edge of the sheet 1501 leaves the roller R3 and timing R34 (time t34) when the leading edge of the sheet 1502 strikes the roller R3. If the rotation of the roller R3 is not reliably stopped during this period, it is impossible to form a sufficient loop for skew correction on the leading edge of the sheet 1502 when the sheet is temporarily stopped at the roller R3.
When the image forming apparatus outputs the sheet 1502 with an erroneous image with a problem such as a skew, the apparatus determines whether the cause of the skew resides on the image forming unit side or the sheet conveyance system side, thereby classifying the causes of the problem.
If the cause of the skew resides on the sheet conveyance system side, physical conditions are checked by examining, for example, at which position on a conveyance path the sheet scratches a conveyance guide or if any problem has occurred on the shape of the conveyance guide.
If there is no problem in the physical conditions, control system conditions are checked by examining whether the rollers constituting a conveyance mechanism rotate/stop (ON/OFF) at proper timings. For example, referring to FIG. 15A, a verification is made on the operation of the roller R3 for sheet skew correction after the trailing edge of the sheet 1501 leaves the roller R3 at timing R33. Although timing R34 when the roller R3 starts stopping is normal, the deceleration time from the instant the roller R3 starts stopping to the instant the roller completely stops is longer than the design value. In this case, the leading edge of the succeeding sheet 1502 strikes the roller R3 before the roller R3 completely stops. This allows to specify that the skew has occurred because a sufficient loop for skew correction has not been formed.
Many steps are required to specify the cause of a phenomenon that has occurred, resulting in deterioration of design efficiency.
With recent advances in the performance of image forming apparatuses, control software itself has become complex. If, therefore, control software includes a defective portion, the number of steps necessary to find the defect, specify its cause, and correct the defect also increases.
In order to decrease the number of such steps, there is an increase in the use of simulation techniques for the design of conveyance mechanisms.
For example, according to the design support technique disclosed in patent reference 1 (Japanese Patent Laid-Open No. 9-81600), there is proposed a system which calculates the behavior of a target conveyance member by simulation, generates a timing chart for conveyance mechanism operation, and displays it, thereby verifying the mechanical operation of the conveyance mechanism.
In addition, patent reference 2 (Japanese Patent Laid-Open No. 5-143260) discloses an arrangement for generating external events, e.g., switching on/off printer control software and opening/closing a cover using an input device such as a keyboard.
Patent reference 1, however, discloses no verification technique for control software for evaluating the setting of a timing for controlling a control target and a change in the state of the control target. The technique disclosed in patent reference 1 can specify the cause of a potential problem in the mechanism but is difficult to specify the cause of a potential problem in software for controlling the mechanism.
The technique disclosed in patent reference 2 is designed to verify a problem in software associated with exceptional processing such as generating an external event, e.g., opening/closing the cover, and shifting the image forming apparatus in a normal operation state to a maintenance state or the like. It is therefore difficult to verify control software for controlling the image forming operation, sheet conveyance operation, and the like of an image forming apparatus and specify the cause of a problem if it has occurred.